Remember a time when you found yourself in a moment of intense, perhaps mortifying stress. For the sake of your mood, try to recall one that you can look back on in laughter. Like that time in your grade seven classroom when a personal, secret-filled note you'd passed to a friend got intercepted and read aloud by your teacher. Or the frightening, startling conclusion to a ghost story told around a campfire. Or when you heard the sirens and saw the flashing lights of a police cruiser as you were coasting along the highway a wee bit too fast.

Can you summon up a memory of the feelings that surged through your body? The heat of blushed cheeks? The raised hair and goosebumps on your neck? The shivers? The butterflies in your stomach?

Many of the odd sensations we feel in the flush of embarrassment or momentary fear arise from the same fight-or-flight response to stress that helps us to survive much more serious, grave threats on our health and well-being.

Take blushing, for instance. Your cheeks tingle and glow with warmth because your body has released adrenaline. This adrenaline surge causes your blood vessels to dilate (vasodilation), improving blood flow, allowing efficient oxygen delivery, and blushing your cheeks with shades from scarlet to salmon. To better understand what happens when we blush, you can think of the word itself as two words packed into one: "blood" and "rush."

All of these adaptations would be helpful in a fight for your life, but what good does it do when you're simply embarrassed? Some experts theorize that blushing is like a red flag for shame. Imagine you're an early human caught overstepping your boundaries in a territorial situation. A blush could be a non-verbal cue to others that says, "Whoops, sorry. Didn't mean to step there!" Blushing could be a shortcut way to show that we understand the social situation we're in. We realize we've made a mistake and we don't want any trouble. Unfortunately, blushing didn't stop that grade seven teacher from reading that tell-all note out loud to the whole class! Oh well, time has passed.

Frequent blushing often accompanies social anxiety, but occasional blushing is a totally natural reaction to stress or embarrassment. Flushing at other times or persistently may indicate an underlying medical condition, such as rosacea. For some people, though, blushing becomes enough of a problem that they choose to get rid of the problem altogether. There's actually a procedure, called endothoracic sympathectomy, in which parts of the nerve chain that stimulate blushing (and excessive sweating) are destroyed.

Goosebumps may also spread across the skin in "hair-raising" moments of high emotion, a tingly wave you feel thanks to the pilomotor reflex. Back in the day, humans faced many predators. When threatened, the pilomotor reflex would kick in and puff out the body hair, making a person appear larger and more imposing. The raised hair also trapped an extra layer of air near the body to retain warmth. We modern humans have retained this porcupine-like reflex. It no longer provides much help during cold snaps, since we don't have as much body hair as our ancient ancestors. So what good does it do us in a stressful moment? Like blushing, you could consider goosebumps another way your body clues you in to stresses or dangers.

When your skin senses cold, you get goosebumps, but when your larger muscles get into the act, you shiver. The tightening and shaking of muscles can make your teeth chatter and generate heat. It's like your body's last-ditch effort to maintain a healthy temperature. As with blushing and goosebumps, shivering alerts us to the impending danger of becoming too cold. But the shaking we do when we're nervous or fearful isn't shivering really: it's trembling. A physiologic tremor happens to everyone now and then, and when aroused by fear or stress, the tremor becomes more noticeable.

Another shaky feeling can come from the fluttering of "butterflies in our stomachs." That tossed-turned-tumbled sensation we sometimes feel can also be tied to our bodies' struggle to survive imminent peril. In the case of butterflies, the peril can be love, embarrassment, fear, worry over a job interview or exam, or any other number of tensions that trigger a release of adrenaline. As adrenaline floods our system, blood gets pulled from where it's not really needed - like in our stomachs - and sent to where it is needed - like to our muscles. A field of medicine called neurogastroenterology studies what some call "the second brain" - the enteric nervous system linking the brain and the gut by way of billions of neurons. Researchers in this field may turn up fresh thinking on the whole butterflies-in-the-stomach phenomenon.

If too many of these fight-or-flight reactions strike you too often and interfere with your day-to-day life, speak to your doctor. Frequent blushing, flushing, trembling, and other stress-related reactions could indicate an anxiety disorder. A recurrently "nervous stomach" may suggest a condition like irritable bowel syndrome.